The present invention relates to a toner for developing electrostatic latent images, employed in printers, copiers facsimile machines, and the like, and to an image forming method using the same.
At present, a method for developing electrostatic latent images, represented by electrophotography, is widely applied to image forming methods which are employed in printers, copiers, facsimile machines, and the like.
This reason is due to the fact that said method is highly completed so that high quality images are consistently obtained at a high speed. However, several problems still remain to be solved. One of said problems is that from the viewpoint of consistent toner fixation, it is necessary to control the molecular weight distribution of toner resins. For example, in order to minimize offsetting at a relatively high temperature, it is necessary to enhance the elastic modulus at said temperature. Therefore, it is preferable to increase high molecular weight components. On the other hand, in order to improve adhesion properties to image forming supports such as paper and the like, it is preferable to increase low molecular weight components. In order to satisfy such contradicting functions, it has been required that the molecular weight distribution is broadened.
On the other hand, from the viewpoint of high image quality, the diameter of toner particles for developing electrostatic latent images is decreased, and further, the particle diameter is desired to be uniform. As methods for producing such toner particle with small diameter, in recent years, development of polymerization methods for producing such a toner has been increasingly performed. Said polymerization methods include a method in which resin particles and colorant particles are subjected to coalescence or salting-out/fusion to prepare irregular-shaped toner particles, a method in which radical polymerizable monomers and colorants are dispersed, followed by being subjected to droplet dispersion into water based medium and the like to obtain the desired diameter of toner particles, and the resultant dispersion undergoes suspension polymerization, and the like.
As noted above, it is necessary that the molecular weight distribution of all resins be regulated to enhance fixability. In order to control the molecular weight distribution, when the molecular weight is decreased utilizing chain transfer agents, employed as suitable chain transfer agents are mercaptan based compounds, especially dodecylmercaptan. However, said components emit specific odor. Accordingly, during heat fixing, residual chain transfer agents volatile to cause a problem of bad smell generation.
Further adhesion property of the toner is not enough and induces disadvantages such as lowering of fixing efficiency and deterioration of off set, and causes image defect such as fogging by variation of charging for use in long period when dodecylmercaptan chain transfer agents are employed.
Said bad smell problem has not been particularly concerned when the so-called pulverization method toner is used, which is prepared by pulverizing block-shaped mixture which is obtained by melt-kneading synthesized resins and colorants followed by cooling the resulting mixture. The inventors of the present invention investigated said problem and discovered that when said polymerization method toner, in which small toner particles were directly prepared, was used, said bad smell caused a problem during image formation.
An object of the present invention is to provide a toner for developing electrostatic latent images, which is prepared employing a polymerization method, is comprised of particles with small diameter, minimizes the generation of a bad smell, causes no bad smell problem and exhibits excellent fixability, and to provide an image forming method using the same.
The other object is to provide a toner for developing electrostatic latent images, which exhibits stabilized charging characteristics and reduced off set phenomenon for long term use.
The object of the present invention is achieved employing the following.
1. In a toner for developing electrostatic latent images, which is comprised of at least a resin and a colorant, a toner for developing electrostatic latent images wherein said toner is comprised of particles having a volume average particle diameter of from 3 to 8 xcexcm, and said resin is obtained by either emulsion polymerization or mini-emulsion polymerization employing as the chain transfer agent thioglycerin or at least one compound selected from compounds represented by the General Formula (1).
HSxe2x80x94R1xe2x80x94COOR2xe2x80x83xe2x80x83(1) 
In the formula, R1 is an aliphatic group having carbon atoms from 1 to 10, which may have a substituent, and R2 is an aliphatic group having carbon atoms from 2 to 15, which may have a substituent.
2. In a toner for developing electrostatic latent images, which is comprised of at least a resin and a colorant, a toner for developing electrostatic latent images wherein said toner is comprised of particles having a volume average particle diameter of from 3 to 8 xcexcm, and said resin is obtained by a suspension polymerization method employing radical polymerizable monomers, as well as thioglycerin or at least one compound selected from compounds represented by the aforementioned General Formula (1), as the chain transfer agent.
3. In an image forming method in which a toner image on an image support, which is formed employing a toner comprised of at least a resin and a colorant, is subjected to heat fixing, an image forming method wherein said toner is comprised of particles having a volume average particle diameter of from 3 to 8 xcexcm, and said resin is obtained by either emulsion polymerization or mini-emulsion polymerization employing as the chain transfer agent thioglycerin or at least one compound selected from compounds represented by the aforementioned General Formula (1).
4. In an image forming method in which a toner image on an image support, which is formed employing a toner comprised of at least a resin and a colorant, is subjected to heat fixing, an image forming method wherein said toner is comprised of particles having a volume average particle diameter of from 3 to 8 xcexcm, and said resin is obtained by a suspension polymerization method, employing radical polymerizable monomers, as well as thioglycerin or at least one compound selected from compounds represented by the aforementioned General Formula (1), as the chain transfer agent.